The invention is in the field of intravascular devices. In particular, the present invention is in the field of intravascular devices used to treat near total and total occlusions in tortuous body lumens.
The majority of intervention procedures such as balloon angioplasty, atherectomy, stenting and the like bring some degree of relief to the patient and improvement in the blood flow. Total or near total occlusions are difficult to treat, however, as intervention tools such as angioplasty balloons are often too large or blunt to cross the occlusion site. This is generally referred to as an inability to cross, and is one of the major causes of failures of occlusion treatment procedures.
Conventional apparatus are typically ineffective in treating total or near total occlusions. One reason for this is that a conventional guidewire may successfully cross the occlusion, but the catheter that is intended to treat the occlusion cannot enter or cross the occlusion because the catheter is of a substantially greater diameter than the guidewire. This situation is illustrated in FIG. 1. Body lumen 110 is shown in cross-section with an occlusion 120 almost totally blocking the flow of fluid through the occlusion. The occlusion 120 may be of various textures and hardnesses, for example soft and fatty or hard and calcified. The occlusion 120 also may be found at a great variety of sites in the body, such as the arterial system including the aorta, the coronary and carotid arteries, and peripheral arteries. As shown in FIG. 1, a balloon catheter 170 includes a catheter shaft 150 and an inflatable balloon 160. The catheter shaft 150 includes an axial lumen 140, indicated by dashed lines. A guidewire 130 is slidably disposed within the lumen 140. Even when the occlusion 120 is particularly hard and calcified or fibrous in nature, the guidewire 130 may succeed in crossing the occlusion 120. However, the catheter with its working element, such as the inflatable balloon 160, may be unsuccessful in following in the path of the small diameter guidewire 130. The entire assembly must then be retracted in the proximal direction and the catheter removed from the patient""s body. Thereafter, other more invasive and traumatic surgical treatment procedures may be necessary to restore a healthy blood flow.
Another reason that conventional apparatus are typically ineffective in treating total or near total occlusions is that conventional catheter shafts and guidewires do not perform well under compressive loading and torque loading. In small and tortuous body lumens, it is often necessary for a physician to push and twist the apparatus in order to navigate the lumen. In typical conventional apparatus the compressive force and torque are not effectively transferred along the length of the apparatus to assist in navigation.
An apparatus for treating occlusions in body lumens is disclosed. In one embodiment, the apparatus includes an outer catheter shaft, an inner catheter shaft slidably disposed in a lumen of the outer catheter shaft, and a guidewire slidably disposed in a lumen of the inner catheter shaft. The distal end of the outer catheter shaft is significantly larger in diameter than the guidewire and the inner catheter shaft. The inner catheter shaft includes an atraumatic, tapered protuberance that increases in diameter from a distal end of the protuberance to a proximal end of the protuberance. The proximal end of the protuberance is approximately the diameter of the distal end of the outer catheter shaft. The guidewire is advanced through the body lumen up to and into the occlusion. The inner catheter shaft is then advanced over the guidewire until the atraumatic, tapered protuberance contacts the occlusion. The outer catheter shaft is then advanced over the inner catheter shaft so that the distal end of the outer catheter shaft closely approaches the proximal end of the atraumatic, tapered protuberance. When the distal end of the outer catheter shaft closely approaches the proximal end of the atraumatic, tapered protuberance, the outer catheter shaft and the inner catheter shaft present a relatively smooth tapering surface to the occlusion such that the outer catheter shaft may enter the occlusion.